1. Field of the Invention
One of the aspects of the present invention relates to an optical scanning apparatus included in an electrophotographic image forming apparatus, and more particularly to a dust-proof mechanism in an optical scanning apparatus.
2. Description of the Related Art
Electrophotographic image forming apparatuses, such as laser beam printers and digital copying machines, include an optical scanning apparatus. The casing of the optical scanning apparatus houses optical elements such as a rotating polygonal mirror, a reflection mirror, and a transmission lens. An optical element becomes dirty due to dust adherence to the optical element, resulting in deterioration of performance of the optical element. For example, for a mirror, the ratio of reflected light amount to incident light amount decreases, while for a lens, the ratio of transmitted light amount to incident light amount decreases. Therefore, to prevent the optical elements from becoming dirty from dust that infiltrates from outside the casing, a transparent member, such as a dust-proof glass, can be arranged on an aperture portion through which scanning light passes.
For example, Japanese Patent Application Laid-Open No. 5-80268 discusses an optical scanning apparatus in which a transparent member is adhesively fixed to an aperture portion of the casing, and laser light is emitted from the transparent member.
One way of cleaning the dirt adhering to the transparent member is to remove the transparent member from the optical scanning apparatus and clean or replace the transparent member. However, removing the transparent member means that the interior of the casing is temporarily open to the outside. Consequently, dust enters into the casing when the transparent member is removed.